The Illyrian deciduous forests form a terrestrial ecoregion of Europe according to both the WWF and Digital Map of European Ecological Regions by the European Environment Agency. It belongs to the biome of Mediterranean forests, woodlands, and scrub, and to the Palearctic ecozone.
The Illyrian deciduous forests stretch along the eastern coast of the Ionian and Adriatic Seas (including the islands) and occupy 40,600 km2 (15,700 sq mi) in Northern Greece, Albania, Montenegro, Bosnia and Herzegovina, Croatia, Slovenia and Northern Italy near Trieste.
The ecoregion is surrounded by the Aegean and Western Turkey sclerophyllous and mixed forests (in Greece), Pindus Mountains mixed forests (in Greece and Albania), Dinaric Mountains mixed forests (in Albania, Montenegro, Bosnia nad Herzegovina, Croatia, Slovenia and Italy) and Po Basin mixed forests (in Italy).
The climate of the ecoregion is mostly of Köppen's Mediterranean type with hot summers (Csa) to humid subtropical with wet winters (Cfa).